1. Field of the Invention
The invention is directed to a method for recording digital data on a magnetic recording medium by use of binary data signals which represent the digital data and magnetic bias signals whose period durations are significantly shorter than a shortest period duration of the data signals. The magnetic bias signals and the data signals are synchronized so that signal edges of the data signals occur simultaneously with signal edges of the magnetic bias signals.
2. Description of the Prior Art:
It is already generally known to employ high-frequency magnetic bias signals when recording digital data on a magnetic recording medium such as, for example, a magnetic disc or a magnetic tape. These magnetic bias signals are overlaid on the data signals and are synchronized with these data signals such that the signal edges of the data signals occur simultaneously with the signal edges of the magnetic bias signals.
In a method disclosed by German published application No. 32 33 489, the direction of the signal edges of the data signals are either the same as, or opposite, the direction of the simultaneously occurring magnetic bias signals. When a signal edge of a data signal is in-phase with the signal edge of a corresponding magnetic bias signal, only a slight shift of the signal edges may occur upon playback of the recorded signal, i.e. the deviation of the occurrence of this signal edge from an anticipated occurrence or point in time is slight. When, however, the signal edge of the magnetic bias signal has an opposite phase, a considerable offset of the signal edge of the recorded signal can occur when the data signals at both sides of the signal edge are allocated to unequal data sequences.
It is disclosed by U.S. Pat. No. 4,420,776, incorporated herein by reference, to generate the magnetic bias signals phase-locked with the data signals and to modify the frequencies of the magnetic bias signals such that every signal edge of the data signals is in-phase with a signal edge of a corresponding magnetic bias signal. This method, however, is relatively involved and is difficult to carry out given some data codings.
Another method is based on the principle of extending a pulse-duration or pulse boundary of the magnetic bias signals between two signal edges of the data signals by half the period duration in order to synchronize the edges of the data signals with the corresponding edges of the magnetic bias signals. This is a relatively simple method. When, however, the frequency of the magnetic bias signals is not much higher than the frequency of the data signals, the missing signal edges of the magnetic bias signals can lead to a higher susceptibility to disturbance in the recorded signals.
It is also possible to apply a method which is based on the employment of a higher-ranking magnetic bias signal whose frequency is an uneven multiple of the maximum frequency of the data signals. The frequency of these higher-ranking magnetic bias signals is then divided by two in order to generate the magnetic bias signals. In such a method, the magnetic bias signals, however, have a DC voltage component since the sum of the pulse durations differs from the sum of the pulse pauses of the magnetic bias signals. This DC voltage component can be utilized to likewise effect a signal edge offset of the recorded signals dependent on the type of coding that is employed for generating the data signals from the digital data.